Method of cooling finely divided materials



June 6, 1961 L. PETERSEN METHOD OF COOLING FINELY DIVIDED MATERIALSOriginal Fil'd Aug. '7, 1956 2 Sheets-Sheet l 33 FIG. I Cg; T

y FM 22M4;%M film/w 7 ATTORNEYS June 6, 1961 PETERSEN METHOD OF COOLINGFINELY DIVIDED MATERIALS Original Filed Aug. 7, 1956 2 Sheets-Sheet 2INVENTOR 6m:

MMKM ATTORNEYS United States Patent 2,987,306 NIETHOD OF COOLING FINELYDlVlDED MATERIALS Louis Petersen, Rye, N. assignor, by mesne assign-This invention relates to the cooling of materials which have beenheated to a high temperature in roasting, calcining, and like operationsand is concerned more particularly with a novel method for effectingcooling of hot material which has been reduced to finely dividedcondition as a result of being burned. Materials of the kind referred toinclude alumina, magnesia, kieselguhr, etc., and, since all theadvantages of the invention are realized in its use in the cooling ofcalcined alumina, the adaptation of the method for that use will beillustrated and described in detail for purposes of explanation.

The cooling of hot alumina burned in a rotary kiln has heretoforecommonly been carried on in rotary coolers and in coolers, which includecooling chambers mounted in planetary arrangement on the kiln near itslower end. In such coolers, the cooling is effected by the passage ofair in contact with the material and the air, which has taken up heatfrom the material, is then conducted into the kiln to take part in theburning operation. Calcined alumina is of such fineness that it isreadily entrained in the stream of cooling air and, as a result, whencoolers of the rotary and planetary chamber types are used, the kilnbecomes so dusty that it is diflicult to control the burning of the fuelto obtain the desired economy. Another disadvantage of such coolers isthe high cost of installation and the loss of heat by radiation. Rotarycoolers are also expensive to maintain and operate.

The present invention is, accordingly, directed to the provision of anovel method of cooling hot materials of great fineness and overcomesthe disadvantages involved in the use of the prior methods abovedescribed. In carrying out the new method, the material issuing from theburning chamber or kiln is introduced into an air stream and issubjected to first-stage cooling while being carried in suspension inthe air to a separator in which the cooled material is separated fromtheheated air. The separated material from the first-stage cooling is thensubjected to a second-stage cooling -by passing it through a cooler ofthe fluid-bed type.

For a better understanding of the invention, reference may be made tothe accompanying drawings, in which:

FIG. 1 is a diagrammatic elevational view of apparatus for practicingone form of the method of the invention in connection with a rotarykiln;

FIG. 2 is a diagrammatic elevational view with parts broken away of aninstallation including apparatus for practicing another form of themethod of the invention; and

FIG. 3 is a diagrammatic perspective view of another kiln installationin which apparatus for practicing the second form of the method of theinvention .is employed.

The installation shown in FIG. 1 includes a rotary kiln "ice 10 having ahood 3, into which the lower discharge end of the kiln projects. Y

The hot burned material discharged from the kiln within the kiln hood 29enters the hopper 30 at the bottom of the hood and is conducted througha pipe 31 containing a counter-weighted flap valve 32 into a stream ofatmosphereic air traveling through a riser pipe 33. The pipe leadsupwardly to the air inlet of a cyclone separator 34 having an air outletat its top, from which a pipe 35 leads. The separator has a solidsoutlet at its bottom, from which the separated solids are lead through apipe 36 into a conveyor 37 of the pneumatic channel type. Such aconveyor comprises a trough and a cover with a porous diaphragm betweenand air is supplied to the trough beneath, the diaphragm through a pipe38. The finely divided material issuing from pipe 36 lands on thediaphragm and is aerated by air ditrused into the material through thediaphragm. As a result, the material becomes fluent and flows down thediaphragm to its lower end.

The air issuing from separator 34 is to be used for combustion in thekiln and, in order to reduce the amount of dust contained therein, thepipe 35 leads to the air intake of a second cyclone separator 39 or to adust collector. The solids separated in the cyclone or dust collectorare conducted from the solids outlet at the bottom thereof through apipe 40 into the conveyor 37 and the air issuing from the separator orcollector is conducted by a pipe 41 to the intake of a fan 42. The fanoutlet is connected by a pipe 43 to a chamber encircling the burner tube45 extending through the hood 29 and the air is used for secondarycombustion in the kiln. However, if desired, part of the air may bedrawn from pipe 43 and used to produce the fuel-primary air mixturesupplied to the burner pipe. A pipe 46 leads from pipe 43 to the riserpipe 33 below the connection of pipe 31 thereto and pipes 43 and 46contain dampers 47, 48, by which the relative amounts of air travelingthrough the two pipes can be controlled. The provision of pipe 46 makesit possible to maintain a fairly constant velocity in the pipe 33 whenthe kiln is operating at different capacities.

The solids discharged from separator 34 and from the separator or dustcollector 39 into the pneumatic conveyor 37 are conducted from theconveyor at its lower end through a pipe 49 into a fluid-bed cooler 50.This cooler may be of the type shown in FIG. 2, which in! cludes ahousing 51 having a material inlet through its top adjacent one end andan outlet 52 for material in an end wall near the top at the oppositeend. Between the inlet and outlet, the chamber is provided with aplurality of vertical partitions 53, so arranged that the materialenering the inlet must travel along a tortuous path before it reachesthe outlet. At the bottom, the housing has an aerating chamber 54 with aporous upper wall 55 and a solid lower wall 56. Air is supplied to thechamber through a supply pipe 57 and the air issues through the pervioustop wall 55 and enters the material within the housing to aerate andfluidize the material. In its travel from the inlet to the outlet, thefluidized material is cooled by a cooling medium traveling through abank of tubes 58, which are of sinuous form and lie between thepartitions within the housing.

In the practice of the method by the apparatus shown in FIG. ,1, the hotburned material issuing from the kiln enters the stream of air travelingthrough the riser pipe conveyed in suspension'to the separator 34. Thesolids removed from the air in the separator enter the pneumatic channelconveyor 37 as does additional material removed from the air streamwithin separator or dust collector 39. The material traveling throughthe conveyor enters the fluid-bed cooler 50, where the second stage ofcooling takes place, and, upon issuance from the cooler 50 through theoutlet 50a, the material has been reduced in temperature to the desiredfinal value.

In the installation of FIG. 2, the burned material dis charged trom thekiln 58 within the hood 59 enters hopper 60, from which it is conductedthrough pipe 61 into a separating device 62. The device includes a tank63 havin g its bottom formed by downwardly convergent aerating chambers64 and the device has an outlet 65 leading from the lower ends of thechambers and containing a gate valve 66. Air is supplied to the aeratingchambers through asupply line 67 and the tank has an overflow pipe 68leading therefrom at a point above the level of the lower end of pipe61. The finely divided constituents of the material entering the device62 are aerated and become fluent therein and the fluidized materialissues through pipe 68, while oversize components sink through theaerated material and enter outlet 65, from which they are dischargedthrough the gate valve 66.

The material issuing through pipe 68 is cooled while being conveyed insuspension in an air stream and, for this purpose, the pipe 68 isconnected to a riser pipe 69 receiving air at its lower end through apipe 70 connected to the outlet of a fan 71. The material carried insuspension upward through the riser pipe enters a separating chamber 72having a bottom outlet for solids, which is connected by a pipe 73 to apneumatic channel conveyor 74 similar in construction and function toconveyor 37. The chamber 72 has an air outlet connected by a pipe 75 tothe inlet of a cyclone separator 76 having a solids outlet at its bottomconnected by a pipe 77 to the conveyor 74. The separator 76 has an airoutlet at its top connected by a pipe 78 to a chamber 79 encircling theburner pipe 80 entering the kiln through hood 59 and the air issuingfrom separator 76 and heated by its contact with the hot material may beused within the kiln either as primary or secondary air of combustion.The material leaving the conveyor 74 at its lower end is conductedthrough a pipe 81 to the inlet of the housing 51 of the fluid-bed coolerpreviously described, where the material undergoes the second stage ofcooling.

In the installation shown in FIG. 3, the material discharged from thekiln 82 within the hood 83 enters a hopper, 84, from which a pluralityof pipes'85 conduct the material to respective separating devices 86,which are similar in construction and operation to the separating device62. Each device 86 has a hopper bottom 87. formed by aerating chamberssupplied with air throughpipes 88 and an outlet 89 containing a rotarygate valve. 90. The

similar to we sit in has an outlet 111 for the cooled material ,1 a

In the practice of the method in the installation of FIG. 3, the burnedmaterial discharged from the kiln undergoes a separation operation inone of the separators 86 and oversize components are removed. The finelydivided material then travels through one of the pipes 91 to enter theair stream in one of the riser pipes 93. The material conveyed insuspension through the riser pipes is subjected to a first stage ofcooling and the solids are removed from the air streams in theseparating chambers 98 and the separators or dust collectors 103 andtransferred by con veyors to the fluid-bed coooler 111, where thematerial undergoes the final stage of cooling. The air heated by contactwith the material is delivered to the chamber 106 and may pass from thechamber into the kiln for use as secondary air of combustion or, ifpreferred, part of the may be utilized as the production of fuel-primarymixture. t

In the installation shown in FIG. 3, as in that of FIG. 2, the fan'forces the air through the riser pipes instead'of drawing the airthrough the system and this arrangement 93 may be put out of operationwhenever the pipe, the

' separating device 86, the separating chamber 98, or the cycloneseparator 103 associated with that pipe require repairs, and thisarrangement offers the further advantage that the number of riser pipesand associated equipment in operation may be varied in accordance withvariations in the kiln capacity. In order to prevent flow through ariser pipe 93, it is only necessary to cut off the air supply to theseparating device 86 delivering material to the pipe and the flow ofmaterial may thus be stopped without the use of mechanical means. Afurther advantage of the 5 installation shown in FIG. 3 is that theriser pipes are of tion Serial No. 602,553, which was filed August 7,1956,

now U.S. Patent No. 2,913,237 as a continuation-in-part of the thenco-pending application Serial No. 477,341, filed December 23, 1954, nowpatent 2,841,384, issued July 1, 1 958.

i I claim:

1. A method of cooling hot burned material in finely divided conditiondischarged from a rotary kiln heated by the combustion in the kiln of afuel-primary air mix ture in the presence of secondary air ofcombustion, which comprises maintaining a stream of air of an initialtemperature not substantially higher than atmospheric, introducingsubstantially all the hot material from the kiln into the air stream,carrying at least the major portion of, the hot material in suspensionby and with thestream for a length of time sufficient to effectsubstantial cooling of the material and heating of the air stream,separating the cooled material from the air stream, and subjecting theseparated material to a second cooling operation by advancing thematerial, while maintaining it in the form of a fluid bed by difiusingan aerating medium into it,

outlet for air connected by a pipe 102 to the inlet of a cycloneseparator 103 having a solids ouflet at its bottom connected to theconveyor by a pipe 104. Each separator 103 has an air outlet at its topconnected by a pipe 105.10. a chamber 106 surrounding the burner pipe107 eirtending through hood 83.into the kiln. Thematerial discharged byconveyor 100 is conducted through pipes 108 containing valves 109 intorespective sections of a fluid-bed cooler 110. Each section of cooler110 may be and subjecting the material in the bed to indirect heatexchange with a cooling medium.

2. The method of claim 1, which includes aerating the hot materialissuing from the kiln under such conditions in a confined space thatoversize pieces of material sink and are withdrawn while the remainderof the material overflows from the space, and introducing theoverflowing material into the stream.

3. The method of claim 1, which includes conveying the separatedmaterial from the point of separation to the fluid bed by pneumaticconveying in which the material 'isaerated and flows by gravity. 7 p 14.The method of claim 1 which includes subjecting the air, from which thematerial was separated, to a second separation to remove materialtherefrom, and combining the solids separated in the two stages andsubjecting the combined solids to a second cooling operation.

5. The method of claim 1, in which the hot material issuing fiom thekiln is divided into a plurality of parts, a plurality of separate airstreams of an initial temperature not substantially higher thanatmospheric are maintained, substantially all of the several parts ofthe hot material are introduced into respective air streams at least themajor proportion of the hot material introduced into each stream iscarried along with the stream in suspension therein for a timesufliciently long to efieet substantial cooling of the material andheating of the stream, the material suspended in each stream isseparated therefrom,

and the separated quantities of material are further cooled by beingadvanced in the form of separate fluid beds being aerated by a gaseousmedium diiiused into the material, the material in the beds beingsubjected to indirect heat exchange with a cooling medium.

References Cited in the file of this patent UNITED STATES PATENTS

